~nai to ～ないと

In Japanese, ~nai to ～ないと generally translates to "if not," or "if [you] don't," or "when [you] don't." It's the i-adjective nai ない plus the conditional to と. Note that it could also be another use of the to と particle, or even a different word, like naito ナイト, "night" or "knight."

Some examples:

• benkyou shinai to daburu
  勉強しないとダブる
  If [you] don't study, [you] will repeat a year.
  • benkyou shinai to ikenai
    勉強しないといけない
    If [you] don't study, [it] can't go. (literally.)
    If [you] don't study, [it will be bad]. (therefore...)
    You must study. You have to study.
    • See also: ~nakucha ～なくちゃ, ~nakya ～なきゃ.
• okane ga nai to komaru
  お金が無いと困る
  If [you] don't have money, [I] will be troubled.
  Without money, [I] will be troubled.
• bakuhatsu shinai to omou
  爆発しないと思う
  [It] won't explode, is what I think. (this isn't the conditional to と, this is the quoting particle.)
  [I] think that [it] won't explode.

Manga: Danna ga Nani wo Itteiru ka Wakaranai Ken 旦那が何を言っているかわからない件

• iwayuru
  otaku (aniota) toiu
  burui de anime wo
  minai to shinu
  seibutsu rashii
  いわゆるオタク（アニオタ）という部類でアニメを見ないと死ぬ生物らしい
  The so-called otaku (anime otaku) type, an organism that dies if it doesn't watch anime, [or so I heard].

Manga: Saiki Kusuo no Psi-Nan, 斉木楠雄のΨ難 (Chapter 72, さわぐ！PK学園文化Ψ（後編）)

• Context: Saiki borrows his father's glasses without permission.
• oi~~ megane kaeshite yo~~
  オイ～～眼鏡返してよ～
  Heey, give [my] glasses back~~
• gaman shite kure chotto me ga "san" ni naru dake daro
  我慢してくれちょっと目が「３」になるだけだろ
  Please endure [it], [all that will happen is that] [your] eyes will become "threes."
  • In anime, eyes are drawn like 3's sometimes when a character that needs glasses isn't wearing them.
• megane ga nai to hotondo mienai-n-da yo~~
  眼鏡がないとほとんど見えないんだよ～
  If [I] don't have [my] glasses, I almost can't see.
  Without [my] glasses [I] almost can't see.
• yon!?
  ４！？
  Fours!?